The objective of this research is to determine how receptive field plasticity in mouse auditory cortex varies across cortical layers. The central hypothesis is that neuronal receptive fields in supra- and infra-granular layers of auditory cortex are complex, highly dynamic transformations of simpler, more stable responses in layer IV. By testing this hypothesis, the proposed experiments will contribute to the development of a model of intracolumnar processing and plasticity in mouse neocortex. The research will proceed in three stages. First, spectrotemporal receptive fields (STRFs) of auditory cortex neurons in different cortical layers will be characterized in awake mice, to see if auditory responses of neurons in supra- and infra-granular layers are more complex than those of neurons in layer IV. Second, the effects of behavioral conditioning on auditory responses in different cortical layers will be examined, to determine whether the STRFs of neurons in supra-and infra-granular layers are more strongly modified by training than those of neurons in layer IV. Third, the effects of nucleus basalis stimulation on auditory responses in different cortical layers will be studied. Nucleus basalis stimulation increases cholinergic input to auditory cortex and induces dramatic plasticity in neuronal receptive fields. This final experiment will describe not only how cholinergic input modifies STRFs in different cortical layers, but also how the layer-specific effects of nucleus basalis stimulation compare to the layer-specific effects of behavioral conditioning.